The invention relates to a process for the production of a locally high, inverse current amplification (upwards current amplification) in a preferably double-diffused or implanted, inversely operated planar transistor which is arranged in a semiconductor body with an integrated circuit.
Digital circuits are known (Valvo-Reports, Volume XVIII, Edition 1/2 pages 215 to 226) which employ the so-called integrated injection logic (I.sup.2 L). The basic gate type of this technique requires only a very small crystal surface and the power loss can be kept extremely low. Bipolar, double-diffused or implanted transistors are used as switching elements. However, in contrast to a transistor of the usual planar technique in an inversely operated transistor, the emitter zone does not lie on the surface of the semiconductor body or an epitaxial layer deposited on a semiconductor substrate, but in the semiconductor body itself, that is to say beneath the surface of the epitaxially deposited layer. Thus an inversely operated npn-transistor has, for example, a n-conducting epitaxial layer, which normally forms the collector of a conventional transistor, forms the emitter, whereas the last n.sup.+ diffusion which normally forms the emitter of the conventional transistor now serves as the collector. This means that the switching element of the I.sup.2 L technique is an inversely operated bipolar npn-transistor in the conventional planar technique.
A fundamental advantage of the integrated injection logic consists in the high packing density which can be achieved on a semiconductor body for the integrated circuit. This is based on the fact that with a corresponding circuit concept, no mutual insulation is necessary. On the other hand, inversely operated transistors have a relatively small upwards current amplification, which here is referred to as upwards current amplification (B.sub.up), which corresponds to the inverse current amplification in normal operation. The upwards current amplification could in fact be improved by a correspondingly high basic doping of the epitaxial layer. However, a high doping of this type is not very effective as it reduces the efficiency of a lateral pnp-transistor as injector (see Valvo-Reports, Vol. 18, Edition 1/2, pages 216 and 217) and at the same time increases the emitter-base-capacitance of the I.sup.2 L- transistor.